PMB: Bacteriology

Question 1

What is bacteriology?

Answer 1

The study of bacterai

Question 2

What are common characteristics of bacteria?

Answer 2

• Prokaryotes
• No nucleus
• Tend to have one chromosome (tho some have more e.g. borrelia burgdorteri)
• Do not look the same
• Microscopoc organisms

Question 3

What are the appearances of bacteria?

Answer 3

• Cocci (spherical)
• Rod (elongated and cylinderical)
  
  • Straight
  • Spiral
  • Curved
• Filamentous
• Dimentions of bacteria vary by species. Single celled different arrangements exiat (different morphologies and how they aggregate differ)

Question 4

How can bacteria colonies be visualised?

How do different species of bacteria differ when visualised this way?

Answer 4

• Using agar plates
• Different species take on different shapes and colours on the same growth medium

Question 5

How is bacteria visualised individually as opposed to as a colony?

Answer 5

• Either using a light microscope at magnification x1000 OR using electron microscopy

Question 6

What is the benefits of using light microscopy?

What can be used to create a better image?

Answer 6

• It is easy to use ad can be provided in most labs
• The use of an oil immersion allows for a sharper image at this magnification

Question 7

What are the benefits and negatives of electron microscopy?

Answer 7

• Gives a much higher quality image
• Not normallt found in general labs as specialist equipment and very expensive
• Very large equipment so may require aother room

Question 8

What are the difficulties with light microspcy?

Answer 8

The image on the right used phase microscopy to view the cells. This requires specialist lenses on microscopes.

To facilitate viewing of bacterial cells it is often easier to use stains

Question 9

Describe the use of dyes for staining?

Answer 9

• Dyes are often used to stain cells to make them easier to see.
• Different dyes exist, each with benefits and disadvantages
• Many rely on cationic organic compounds combining with the negatively charged cell envelope

Question 10

What is the most common method for staining bacteria?

Answer 10

Gram Staining

Question 11

Describe Gram staining

Answer 11

• Several different steps involved, but reaults in batceria being stained one of 2 colours
• Not all bacteria will stain equally

Question 12

What can Gram staining be used for?

Answer 12

• Tool for classifcation of bacteria
  
  • Red/pink = Gram -ve
  • Purple = Gram +ve
• Used to roughly see if there is comtamination in bacteria cultures
  
  • Colour stained depends on +/- and shape so if both the same unable to use this

Question 13

What are gram-variable organisms?

Answer 13

Normally for a species of bacteria there is a pacrticular staining pattern

However, some bacteria change cell wall strruce in different growth conditiond leading to a difference in gram staining - these are Gram-variable organisms

Question 14

Describe the structure of bacteria including the layers it is composed off

Answer 14

• Unicellular
• Capsule, cell wall, plasma membrane, cytoplasm

Question 15

Explain the purpose of the cell wall

Answer 15

• Solutes dissolved in the cytoplasm of bacteria creates osmotic pressure outwards
• This pressure is great enough to rupture the cell
• Therefore the cell wall is used to prevent this and provide strength and rigidity to the cell
• It influences the shape of the cell

Question 16

What is the bacteria cell made off?

Answer 16

• Peptidoglycan - gives the cell strength
• Peptidoglycan is composed of 2 glucose derviatives and AAs
• The glucose derviatives are called NAG and NAMA or NAM
• The amino acids and glucose derivatives form repeating units called glycan tetrapeptides. These monomer units join together to form the polysaccharide peptidoglycan

Question 17

What is the difference between Gram + and - bacteria

Answer 17

• Positive
  
  • Postive has a thicker peptidoglycan layer and a larger range
  • Has techoic acids
• Negative
  
  • Thinner peptidoglycan layer
  • Lacks techoic acids
  • extra layer: LPS

Question 18

Describe the LPS layer

Answer 18

• It surrounds the Petidoglycan layer and cytoplasmic membrane
• Contains protiens
• exists as a Bilayer
• lipids are highly glycosylated
• It is endotoxin

Question 19

What does it mean by the LPS being endotoxin?

Answer 19

Endotoxin is pyrogenic - which means causes a fever

Question 20

what are bacteria endospores?

What kills them?

Answer 20

• Some bacteria species produce interal spores called endo spores e.g. baccillus or Clostridium
• These endospores are resistant to heat (100C), UV, gamma and many chemicals/ antimicrobilas therefore can survive for long periods of time in an enviroment.
• Autoclvaing at 121C kills them
• Endospores have a higly complex structure and multiple layers

Question 21

What layers are endospores made up off?

Answer 21

Outer layer is the exosporium

Then the spore coat made from peptidoglycan

Then the cortex, which is rich in proteins

Then the core which contains the protoplasm with bacteria DNA and associated enzymes required for DNA replication

Question 22

What is the purpose of endospores?

Answer 22

Allows bacteria to survive in harsh conditions for a long period of time. When more favourable conditions arise they can return to normal vegetative lifecylce

Question 23

What is the core of a endospore contain?

Answer 23

It is rich in 2,6 dicarboxylic acid/ calcium ion complex which helps with urvial

Question 24

How are endospores visulaised?

Answer 24

Gram staining doesn’t work so schaeffer-fulton is used. This method of staining uses malachite green.